DON EMMERT/AFP/Getty Images(NEW YORK) -- It has not yet been confirmed whether Adam Lanza had been diagnosed with mental illness, but the 20-year-old, who murdered his mother, then drove to a Newtown, Conn., elementary school and gunned down 20 first-graders and six adults, has again shined the spotlight on care for the mentally ill in the United States, and has many asking whether yet another mass shooting could have been prevented.

Despite four shooting rampages since President Obama took office in 2009, mental health care continues to be hampered by budget cuts, closures, battles with insurers and stigma, doctors said.

"We have very good treatments for mental illness that are highly effective," said Dr. Jeffrey Lieberman, president-elect of the American Psychiatric Association. "But they're not widely available. People don't have ready access to them."

Since the recession forced budget cuts in 2009, state general funding for mental health care has decreased by an estimated $4.35 billion nationwide, according to the National Association of State Mental Health Program Directors, which serves 6.8 million patients a year.

Since 2009 alone, 3,222 psychiatric hospital beds are no longer available to patients, and another 1,249 may disappear soon because of proposed closures, according to the association. That's about 10 percent of all state psychiatric hospital beds gone in about three years, said Dr. Robert Glover, the association's executive director, who said he'd never been more worried.

"This is the worst I've seen it," Glover, who's worked in mental health for almost five decades, said about the cuts. "They are painful, and unbelievably tough. I am incredibly worried about future cuts with the fiscal cliff and state budgets not getting better."

One in five American adults reported suffering from mental illness within the past year, with one in 20 reporting serious mental illness that resulted in "functional impairment," according to the Substance Abuse and Mental Health Services Administration's latest annual National Survey on Drug Use and Health Report.

Despite its prevalence, mental illness is something patients and those around them have tried to ignore dating as far back as World War I, when soldiers were called cowards for showing signs of what we now know was post traumatic stress disorder, Lieberman said.

Today, the largest mental health facilities are for inmates at the Los Angeles County Jail in California, Cook County Jail in Illinois and Rikers Island in New York, Lieberman said.

According to the Bureau for Justice Statistics, 56 percent of state prisoners, 45 percent of federal prisoners and 64 percent of jail inmates had mental health problems in 2006. Between 10 percent and 20 percent of those with mental health problems had symptoms of psychosis, such as delusions or hallucinations.

Most mentally ill patients aren't dangerous, but it's very difficult for psychiatrists to predict who will become violent, said Dr. Carol Bernstein, a psychiatry professor at NYU Langone Medical Center.

The high number of prisoners with mental illness is a mark of the failures of the current mental health care climate, because the mentally ill wind up behind bars before they can get treatment, Lieberman said.

"We haven't provided these people with what they need," said Lieberman. "What we're seeing here now is, 'Uh, oh people have mental health problems. We need to pay attention to mental illness now.' But it's a too little, too late kind of reaction to this. ...Whatever it takes is worth it, but this is kind of late in the game."